Chronic tendinopathies and enthesopathies are common musculoskeletal conditions in orthopedics and sports medicine, frequently leading to pain, impaired function, and significantly reduced quality of life. Their pathogenesis involves tissue degeneration and ineffective repair response, often without an active inflammatory process.

Standard conservative management based on physiotherapy and activity modification is often prolonged and not always satisfactory. Minimally invasive injectable interventions supporting tendon and enthesis regeneration represent a promising alternative due to their favorable safety profile and outpatient feasibility.

Hyaluronic acid (HA) is a glycosaminoglycan naturally present in connective tissues. In the context of tendinopathy, it is thought to modulate inflammatory processes, provide mechanical protection by reducing friction and adhesion within the tendon sheath, and support the proper organization of collagen fibers in the tendon matrix.

Platelet-rich plasma (PRP) is an autologous concentrate of platelets providing high local concentrations of growth factors, including platelet-derived growth factor (PDGF), transforming growth factor beta (TGF-β), and vascular endothelial growth factor (VEGF), which initiate and support repair processes, cellular proliferation, and angiogenesis.

This prospective, randomized, open-label, two-arm study aims to compare the clinical efficacy of hyaluronic acid (HA) and platelet-rich plasma (PRP) injections in 80 participants with chronic Achilles tendinopathy or medial epicondylopathy of the elbow. Participants will be randomly assigned in a 1:1 ratio to receive either two HA injections or two PRP injections administered two weeks apart under ultrasonographic guidance. Follow-up will continue for 12 months after the second injection. The primary outcomes are the changes from baseline to 6 months in pain intensity measured using a 100-millimeter (mm) Visual Analog Scale (VAS), upper-limb function measured using the Quick Disabilities of the Arm, Shoulder and Hand (QuickDASH) questionnaire in participants with medial epicondylopathy, and Achilles tendon symptoms and function measured using the Victorian Institute of Sport Assessment-Achilles (VISA-A) questionnaire in participants with Achilles tendinopathy. The results will provide evidence to support the selection of injectable treatment for chronic tendinopathies and enthesopathies.